Impaired glucose tolerance is a hallmark of aging even in the absence of attendant pathology, and is associated with increased mortality due to enhanced risk for development of diabetes and cardiovascular disease. Intolerance of aging is typically attributed to the development of insulin resistance, resulting from changes in adiposity, diet, and/or sedentary lifestyle, and studies to understand the pathogenesis of intolerance have focused on the relative contributions of insulin resistance and pancreatic islet dysfunction. We have demonstrated that insulin-independent mechanisms of glucose regulation are equally important in determining glucose tolerance. These processes, termed "glucose effectiveness", are defined as the actions of glucose to regulate its own utilization (Rd) and hepatic production (HGO) independent of elevated insulin. The purpose of this proposal is to examine the role of glucose effectiveness in the glucose intolerance of normal, non-diseased aging in the rat. We will test the hypothesis that in insulin-resistant states such as aging, efficient disposition of a carbohydrate challenge becomes increasingly dependent on metabolic factors which are independent of insulin action, i.e. glucose effectiveness. These studies will establish the role of glucose effectiveness in the glucose intolerance of normal, non-diseased aging. We will apply newly developed methods to quantify glucose effectiveness directly in young and old rats, and determine how aging alters the relative contributions of Rd vs HGO and the specific tissue sites and glucose transporters involved. We will examine the mechanisms by which glucose effectiveness may compensate in aging-associated insulin resistance. Finally, we propose to examine the ability of caloric restriction to improve tolerance through their actions on glucose effectiveness, and determine the tissue sites, mechanisms, and glucose transporters which may be involved.